ESP8266 NodeMCU on battery power web LED - YouTube
IoT Based Battery Status Monitoring System using ESP8266
Power ESP32/ESP8266 with Solar Panels and Battery | Random Nerd Tutorials
NodeMCU Dev Kit with ESP8266, WiFi and Battery Holder | Paradisetronic.com
lua - Check the battery status with NodeMCU? - Stack Overflow
Fredrik Olofsson on Twitter: "Battery powered #esp8266 logging its battery voltage for 12h now. From 3.05V to 2.99V https://t.co/SlSGIfGcxn http://t.co/aJmUoJJ32T" / Twitter
ESP8266-12 board with battery holder - ESP-12BATTERY
Seven Pro Tips for ESP8266 : 9 Steps (with Pictures) - Instructables
Design your own ESP Board for Battery Powered IoT Applications